When using an endoscope for optical monitoring in high-frequency surgery, the difficulty can occur, undesirably, that voltage pulses produced are transferred, via the endoscope, all the way to the optical recording device fixed to the endoscope. These voltage pulses can lead to a deterioration in the recording of the image with the image sensor of the optical recording device. In CCD sensors, this can lead to a particularly grainy image. If CMOS sensors are used, even a total image drop-out can occur, in particular because of digital signal processing.